/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_iir_lattice_q31.c
 * Description:  Q31 IIR Lattice filter processing function
 *
 * $Date:        18. March 2019
 * $Revision:    V1.6.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"

/**
  @ingroup groupFilters
 */

/**
  @addtogroup IIR_Lattice
  @{
 */

/**
  @brief         Processing function for the Q31 IIR lattice filter.
  @param[in]     S          points to an instance of the Q31 IIR lattice structure
  @param[in]     pSrc       points to the block of input data
  @param[out]    pDst       points to the block of output data
  @param[in]     blockSize  number of samples to process
  @return        none

  @par           Scaling and Overflow Behavior
                   The function is implemented using an internal 64-bit accumulator.
                   The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
                   Thus, if the accumulator result overflows it wraps around rather than clip.
                   In order to avoid overflows completely the input signal must be scaled down by 2*log2(numStages) bits.
                   After all multiply-accumulates are performed, the 2.62 accumulator is saturated to 1.32 format and then truncated to 1.31 format.
 */

void arm_iir_lattice_q31(
	const arm_iir_lattice_instance_q31 *S,
	const q31_t *pSrc,
	q31_t *pDst,
	uint32_t blockSize)
{
	q31_t *pState = S->pState;                       /* State pointer */
	q31_t *pStateCur;                                /* State current pointer */
	q31_t fcurr, fnext = 0, gcurr = 0, gnext;        /* Temporary variables for lattice stages */
	q63_t acc;                                       /* Accumlator */
	q31_t *px1, *px2, *pk, *pv;                      /* Temporary pointers for state and coef */
	uint32_t numStages = S->numStages;               /* Number of stages */
	uint32_t blkCnt, tapCnt;                         /* Temporary variables for counts */


	/* initialise loop count */
	blkCnt = blockSize;

#if defined (ARM_MATH_DSP)

	/* Sample processing */
	while (blkCnt > 0U) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fcurr = *pSrc++;

		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];

		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];

		/* Initialize state read pointer */
		px1 = pState;

		/* Initialize state write pointer */
		px2 = pState;

		/* Set accumulator to zero */
		acc = 0;

		/* Process sample for first tap */
		gcurr = *px1++;
		/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
		fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));

		/* gN(n) = kN * fN-1(n) + gN-1(n-1) */
		gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));

		/* write gN-1(n-1) into state for next sample processing */
		*px2++ = gnext;

		/* y(n) += gN(n) * vN */
		acc += ((q63_t) gnext * *pv++);

		/* Update f values for next coefficient processing */
		fcurr = fnext;


#if defined (ARM_MATH_LOOPUNROLL)

		/* Loop unrolling: Compute 4 taps at a time. */
		tapCnt = (numStages - 1U) >> 2U;

		while (tapCnt > 0U) {
			/* Process sample for 2nd, 6th ...taps */
			/* Read gN-2(n-1) from state buffer */
			gcurr = *px1++;
			/* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
			/* y(n) += gN-1(n) * vN-1  */
			/* process for gN-5(n) * vN-5, gN-9(n) * vN-9 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-1(n) into state for next sample processing */
			*px2++ = gnext;

			/* Process sample for 3nd, 7th ...taps */
			/* Read gN-3(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 3rd, 7th .. taps */
			/* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */
			fcurr = __QSUB(fnext, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fcurr * (*pk++)) >> 31));
			/* y(n) += gN-2(n) * vN-2  */
			/* process for gN-6(n) * vN-6, gN-10(n) * vN-10 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-2(n) into state for next sample processing */
			*px2++ = gnext;

			/* Process sample for 4th, 8th ...taps */
			/* Read gN-4(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 4th, 8th .. taps */
			/* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
			/* y(n) += gN-3(n) * vN-3  */
			/* process for gN-7(n) * vN-7, gN-11(n) * vN-11 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-3(n) into state for next sample processing */
			*px2++ = gnext;

			/* Process sample for 5th, 9th ...taps */
			/* Read gN-5(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 5th, 9th .. taps */
			/* fN-5(n) = fN-4(n) - kN-4 * gN-1(n-1) */
			fcurr = __QSUB(fnext, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-4(n) = kN-4 * fN-5(n) + gN-5(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fcurr * (*pk++)) >> 31));
			/* y(n) += gN-4(n) * vN-4  */
			/* process for gN-8(n) * vN-8, gN-12(n) * vN-12 ... */
			acc += ((q63_t) gnext * *pv++);

			/* write gN-4(n) into state for next sample processing */
			*px2++ = gnext;

			/* Decrement loop counter */
			tapCnt--;
		}

		fnext = fcurr;

		/* Loop unrolling: Compute remaining taps */
		tapCnt = (numStages - 1U) % 0x4U;

#else

		/* Initialize blkCnt with number of samples */
		tapCnt = (numStages - 1U);

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */

		while (tapCnt > 0U) {
			gcurr = *px1++;
			/* Process sample for last taps */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));

			/* Output samples for last taps */
			acc += ((q63_t) gnext * *pv++);
			*px2++ = gnext;
			fcurr = fnext;

			/* Decrement loop counter */
			tapCnt--;
		}

		/* y(n) += g0(n) * v0 */
		acc += ((q63_t) fnext * *pv++);

		*px2++ = fnext;

		/* write out into pDst */
		*pDst++ = (q31_t)(acc >> 31U);

		/* Advance the state pointer by 4 to process the next group of 4 samples */
		pState = pState + 1U;

		/* Decrement loop counter */
		blkCnt--;
	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCur = &S->pState[0];
	pState = &S->pState[blockSize];

	/* Copy data */
#if defined (ARM_MATH_LOOPUNROLL)

	/* Loop unrolling: Compute 4 taps at a time. */
	tapCnt = numStages >> 2U;

	while (tapCnt > 0U) {
		*pStateCur++ = *pState++;
		*pStateCur++ = *pState++;
		*pStateCur++ = *pState++;
		*pStateCur++ = *pState++;

		/* Decrement loop counter */
		tapCnt--;
	}

	/* Loop unrolling: Compute remaining taps */
	tapCnt = numStages % 0x4U;

#else

	/* Initialize blkCnt with number of samples */
	tapCnt = (numStages - 1U);

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */

	while (tapCnt > 0U) {
		*pStateCur++ = *pState++;

		/* Decrement loop counter */
		tapCnt--;
	}

#else /* #if defined (ARM_MATH_DSP) */

	/* Sample processing */
	while (blkCnt > 0U) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fcurr = *pSrc++;

		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];

		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];

		/* Initialize state read pointer */
		px1 = pState;

		/* Initialize state write pointer */
		px2 = pState;

		/* Set accumulator to zero */
		acc = 0;

		tapCnt = numStages;

		while (tapCnt > 0U) {
			gcurr = *px1++;
			/* Process sample */
			/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
			fnext = clip_q63_to_q31(((q63_t) fcurr - ((q31_t)(((q63_t) gcurr * (*pk)) >> 31))));

			/* gN(n) = kN * fN-1(n) + gN-1(n-1) */
			gnext = clip_q63_to_q31(((q63_t) gcurr + ((q31_t)(((q63_t) fnext * (*pk++)) >> 31))));

			/* Output samples */
			/* y(n) += gN(n) * vN */
			acc += ((q63_t) gnext * *pv++);

			/* write gN-1(n-1) into state for next sample processing */
			*px2++ = gnext;

			/* Update f values for next coefficient processing */
			fcurr = fnext;

			tapCnt--;
		}

		/* y(n) += g0(n) * v0 */
		acc += ((q63_t) fnext * *pv++);

		*px2++ = fnext;

		/* write out into pDst */
		*pDst++ = (q31_t)(acc >> 31U);

		/* Advance the state pointer by 1 to process the next group of samples */
		pState = pState + 1U;

		/* Decrement loop counter */
		blkCnt--;
	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCur = &S->pState[0];
	pState = &S->pState[blockSize];

	tapCnt = numStages;

	/* Copy data */
	while (tapCnt > 0U) {
		*pStateCur++ = *pState++;

		/* Decrement loop counter */
		tapCnt--;
	}

#endif /* #if defined (ARM_MATH_DSP) */

}

/**
  @} end of IIR_Lattice group
 */
